FirebaseAuth is not Initialized

I want to add firebase login system in my app. I use Firebase Authentication and Firebase Core for it.
But I Got Error FirebaseAuth is not Initialized
I Add .Json file too and also checked UseJsonFile box.

Here is blocks I use

Is This Configuration OK?

Pls Help me to Resolve this issue.

(I Already search over community but not get satisfactory answer)

Have you added package name and sha -1 key on Firebase

I Already Added Package Name and SHA1 Key But still face this issue

I Use this SHA key to Firebase. Is it OK?

Yes its ok